I'd be interested in this when it is ready - as I mentioned elsewhere in the thread, I will have an off-site system with identical hardware for redundancy.
You might want to check out this thread. I've finally finished a set of articles that describe what I had in mind. Maybe it is of use to you.
Although 22TB data is several times more data than what I have, you could buy 7+2 Hitachi 3TB HDDs for a RAIDZ2 setup and it would cost $1260. I realize you probably already have tape drive (starting at $1500 on newegg). As a comparison, if you have 5 free SATA ports that support port multiplication, you only have to buy 5* e-SATA docks for something like $15/ on ebay plus some SATA data + power connectors that would cost a total of about $100 all up. For each backup HDD pool, you'd want silicone covers for each HDD ($4 per HDD) and a padded camera bag for $60-$80.
You could probably have 3 backup HDD pools before tape starts being cheaper.